Abstract: Objective: To investigate the impact of individual body size factors and tissue composition on the size-specific dose estimate(SSDE_WED) based on water equivalent diameter for adult chest. Methods: A total of 205 adult subjects who underwent chest CT scans at our hospital were enrolled, and their individual information (height, weight, body mass index) was collected. The average CT_ROI value, cross-sectional area A_ROI, transverse diameter, and anteroposterior diameter of the thorax on the axial images at the intermediate level were collected. The fat content, fat volume, muscle content, and muscle volume across the entire scanning range were recorded. The anteroposterior diameter/transverse diameter, scan length, and scan length/transverse diameter were calculated. The volume CT dose index (CTDI_vol) of the subjects was obtained, and the SSDE_WED values at the mid-level of all subjects were calculated. The correlations between fat content, muscle content, fat volume, muscle volume, BMI, cross-sectional A_ROI, transverse diameter, anteroposterior diameter, scan length, scan length/transverse diameter ratio, anteroposterior diameter/transverse diameter ratio, and SSDE_WED were analyzed. Results: Fat content, fat volume, muscle volume, BMI, cross-sectional AROI, transverse diameter, anteroposterior diameter, scan length/transverse diameter ratio are significantly positively correlated with SSDEWED. Muscle content, anteroposterior/transverse diameter ratio, and scan length showed no correlation with SSDE_WED. Conclusion: Multiple individual body size factors and tissue compositions are significantly correlated with SSDE_WED, among which adipose tissue is the key factor influencing SSDE_WED.